This invention pertains to an electrolytic capacitor having a glass-to-metal seal, and more particularly a compression seal. The seal of this invention has a washer bonded to a compression ring and to a mass of glass containing a tubular feed-through. The outer side of the washer is bonded to an end of a capacitor casing around the periphery of both.
Glass-to-metal hermetic seals are well-known in the capacitor art. These seals are of two main types: matched seals in which the coefficients of expansion of the glass and metal members are substantially the same, giving a strain-free seal; and compression seals in which the glass and central metal terminal are retained under compression by an outer metal member, usually a ring.
Unfortunately, matched seals are fairly fragile and can be easily damaged. Prior compression seals generally have had a central glass mass containing a feed-through surrounded by a metal eyelet or ring which compresses the glass. There has been a problem of corrosion or attack of the ring by the electrolyte, and plated and clad rings and/or eyelets have been used as a result.
Plated materials have been unsatisfactory generally because of pinholes present or developing in the plating. Clad members are more expensive, and the designs of seals incorporating them have been bulky.